This invention relates to lasers and, more particularly, to an improved output mirror for far infrared lasers.
Recently developed optically pumped far infrared lasers have produced numerous new laser lines in the spectral region from about 40 to 1800 microns. Optically pumped far infrared lasers have optical problems given rise to by the fact that the optics must simultaneously have certain desired properties as two widely separated infrared and far infrared wavelengths. For purposes of this application, the infrared portion of the spectrum is defined as the range of wavelengths between about 1-40 microns and the far infrared portion of the spectrum is defined as the range of wavelengths between about 40-1300 microns.
In a far infrared waveguide laser, a selected carbon dioxide laser line, typically around 10 microns wavelength, is focused through a hole in an input mirror into a waveguide resonator containing a gas to be pumped. To enhance efficiency, it is necessary that the pumping radiation reflect back and forth until it is fully absorbed by the gas. This requires that both mirrors at the ends of the laser cavity be highly reflective at the carbon dioxide laser wavelength. At the same time, the mirror which serves as the output mirror must be partially transmitting, to a desired degree, of the far infrared laser wavelength, to uniformly couple out the far infrared resonator mode in a diffraction limited output beam. To applicant's knowledge, there has not heretofore been constructed an efficient mirror that will reflect substantially all of the radiation over the range of about 9.6 to 10.6 micron bands of the carbon dioxide pump laser, and partially transmit a specified fraction (typically 0 to 40%) of the radiation at the far infrared laser wavelengths.
Various types of high reflectance coatings have been utilized in optics for many years and it is known in the art that one can fabricate a reflecting mirror for the 10 micron wavelength by applying layers of certain dielectric materials on a semiconductor substrate. While this expedient is suitable for obtaining reflectance of the pump laser wavelength, this structure does not, in general, provide the desired partial reflectance at the far infrared wavelength.
Metal meshes or grids have been found to be good reflectors and partially transmitting mirrors for the far infrared. By varying the mesh spacing and mesh strip width relative to the wavelength, power reflectances between 0 and 100% can be achieved, as desired. These structures, however, do not provide the necessary high reflectance of the pump laser wavelength.
It is an object of the present invention to provide solution to the prior art problems as set forth.